The invention relates to radio and television receivers and in particular to indicators for displaying the radio frequency of a station to which the receivers are tuned.
Numerous popular entertainment devices, such as television and AM and FM radios, utilize radio frequency receivers to detect and reproduce in audible form radio frequency signals transmitted by distant broadcast stations. These receivers are generally tuned to select one of a number of stations by setting the resonant frequency of an oscillator in the receiver to a frequency which differs from the frequency of the signal transmitted from the station by a predetermined fixed amount. In conventional receivers, the resonant frequency of the oscillator can be continually varied for detection of all stations in a band of frequencies, for example, by varying the capacitance of a capacitor in the oscillator circuit. Coupled to the capacitor is a tuning indicator, which moves as the capacitance is changed, to identify the frequency of the station to which the receiver is tuned.
Many types of tuning indicators have been used in the past. In one type of indicator, the frequencies are imprinted on a disc rotatably coupled to the capacitor. As the capacitance is changed, the disc moves relative to a window positioned in the receiver through which the frequencies of the stations can be observed. In a second type of indicator, the frequencies are imprinted on a fixed scale and a pointer is arranged to move relative to the fixed scale as the receiver is tuned. These indicators, however, are often difficult to read and do not always provide an accurate indication of the frequency of the station being received.
Recently, digital displays have been introduced for a variety of applications. An example is an "Optical Display Digital Watch" disclosed in U.S. Pat. No. 3,566,602 to Bergey et al, of Mar. 2, 1971 wherein the time is displayed in digital form in a display window. Fiber optic bundles are interposed between the display window and minute and hour wheels, having indicia representative of the time which are driven by the watch movement, and provide light transmission paths for displaying the time indicia, from the minute and hour wheels, in the display window. While this type of display is relatively easy to read, the watch disclosed in the above-referenced patent provides a continuous display and has no provisions for accurately aligning the time information with the fiber optic bundle.
In accordance with the present invention, a tuning indicator for a radio frequency receiver produces a digital display of the frequencies of received broadcast stations which is accurate and relatively easy to read and is displayed only when the receiver is tuned to a station.